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https://issues.apache.org/jira/browse/CASSANDRA-1391?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13180527#comment-13180527
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Jonathan Ellis commented on CASSANDRA-1391:
-------------------------------------------

While getting rid of avro is great, replacing "serialize to avro" with 
"serialize to thrift" isn't as much improvement as I was hoping for.  I thought 
we were on board with modeling the schema "natively" in system columnfamilies 
as sketched in 
https://issues.apache.org/jira/browse/CASSANDRA-1391?focusedCommentId=13149875&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-13149875.
  Which would allow the apply/diff design I keep talking about instead of 
having to do that manually in UCF, allow dropping the last_migration_key 
indirection, pave the way for CASSANDRA-2477, and probably more simplifications.

Is there a reason that doesn't work?
                
> Allow Concurrent Schema Migrations
> ----------------------------------
>
>                 Key: CASSANDRA-1391
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-1391
>             Project: Cassandra
>          Issue Type: Improvement
>          Components: Core
>    Affects Versions: 0.7.0
>            Reporter: Stu Hood
>            Assignee: Pavel Yaskevich
>             Fix For: 1.1
>
>         Attachments: 
> 0001-new-migration-schema-and-avro-methods-cleanup.patch, 
> 0002-avro-removal.patch, 
> 0003-oldVersion-removed-new-migration-distribution-schema.patch, 
> CASSANDRA-1391.patch
>
>
> CASSANDRA-1292 fixed multiple migrations started from the same node to 
> properly queue themselves, but it is still possible for migrations initiated 
> on different nodes to conflict and leave the cluster in a bad state. Since 
> the system_add/drop/rename methods are accessible directly from the client 
> API, they should be completely safe for concurrent use.
> It should be possible to allow for most types of concurrent migrations by 
> converting the UUID schema ID into a VersionVectorClock (as provided by 
> CASSANDRA-580).

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